Feature Request

Crates

tracing-serde

Motivation

Currently, tracing-serde supports serializing tracing types, such as Metadata, Event, span::Attributes and span::Record, etc. However, it does not support deserializing those types from a serialized representation. It would be good to support this.

Proposal

We should add structs to tracing-serde that represent the deserialized form of tracing types that can currently be serialized. These would have public accessors returning the fields of those types, and implement the serde::Deserialize trait.

Alternatives

From the outside, it might seem like we should just implement serde::Deserialize for tracing-core types like Metadata, Event, et cetera, rather than adding new structs that those types can be deserialized as. However, there are some serious issues with this. tracing structs like Event and Metadata consist primarily of references to other data for performance and space optimization reasons. Similarly to how we don't serialize the internal representations of types like ValueSet and instead use SerializeMap etc, we wouldn't want to deserialize internal representations that don't make sense outside of the address space of the process where they originated.

Another option is to not implement Deserialize for any structs, and just change all Serialize implementations to serialize data structures like maps and sets. This would mean removing all uses of SerializeStruct and replacing it with unstructured data. However, this makes using deserialized tracing data more difficult for users, as rather than having a nice structured API for well-known fields, everything is represented as unstructured maps that may or may not contain particular values or types.